1. Technical Field
The invention relates to a method and apparatus for measuring the rotary movement of a shaft, wherein according to said method voltage pulses are generated in a detecting head by inductively scanning a magnetic pattern radially applied to a magnetic disk, the voltage pulses being associated with said magnetic pattern and used for determining the rotary movement of a shaft.
2. Background Art
An apparatus of the generic type is known, for example, from EP 0 048 983 in which for determining rotational speed and phase angle of rotating bodies a detector means is used consisting of a magnetic recording medium attached to the body to be measured and having circular tracks provided with N and S magnet poles. Said tracks may also be formed as thin layers as disclosed in EP 0 048 983. For detecting either rigidly mounted coils or magnetic resistor elements are used which are arranged in a reference position invariable relative to the track.
From EP 0 474 362, a speedometer which is known for determining the angular velocity of a rotating object is provided with two encoders stationarily arranged about the shaft of the rotating object to be measured and generating pulses of different resolution according to the rotation of the shaft.
SU-PS 758176 discloses a controlled delay unit with which stable pulses having a fixed frequency were applied to a magnetic disk which is scanned and the signals are converted into a correspondingly proportional voltage. In this way, speed deviations can be detected and used for controlling the disk-to-playback head distance along a guide.
DE-OS 31 15 670 discloses a method for determining the angular position of magnetic heads relative to a recording tape. In addition to the magnetic heads, a head wheel has two rotating permanent magnets which during rotation generate pulses of changing polarity in a stationary coil arranged adjacent to the head. The pulses are used for determining the respective position and speed of the head wheel disk.
The above mentioned apparatus have a disadvantage in that the measuring accuracy for determining the rotational speed or angular position of the rotating part is, due to their construction, predetermined and cannot be altered. On the one hand, for a highly precise speed determination thus a lot of instruments are required, such as in the case of EP 0 474 362, on the other hand, such a sophisticated instrumentation is not necessary for measurements requiring lower resolution.